1. Field of the Invention
The present invention relates to flame retardants for use in resins and methods of use of the flame retardants. Specifically, the invention relates to polybromoaryl ethers and the methods of use of said ethers as flame retardant additives for use in resins, including polyamides, and methods of use of the flame retardants.
2. Description of the Background Art
Various additive materials are used in formulations with polymer resins during compounding to augment or affect the properties of the final compositions. Among these additives, flame retardants are added to polymer resins to reduce the flammability. The use of flame retardant materials may adversely affect the polymer properties, depending on the specific system being used. The effect of the flame retardants on these polymer properties can sometimes be minimized by using a more efficient flame retardant that can be utilized at a lower lead level verses other flame retardant materials. The class of flame retardants known as polybromoaryl ethers are more efficient in polyamide resins than the standard brominated polystyrene type of materials and can be used at a lower loading to achieve the same level of flame retardancy, while having less of an impact on the overall properties of the system.
These polybromoaryl ethers are very thermally stable materials. As a result, they provide improved thermal properties to the resin systems in which they are employed. By producing a polybromoaryl ether with lower ionic impurities, the improved thermal properties can be realized even further. This provides improved properties, such as producing less “off-gassing” during injection molding and by also providing an improvement by minimizing the “blistering” of parts made with these types of materials.
The molecule commercially known as PO-64, or PO-64P was invented in our laboratories in the late 1970s (then known as Velsicol Chemical Corporation) and was promoted for use in polyamides. This material is a polybromoaryl ether and was made by the polymerization of tribromophenol in an aqueous medium and is still made today by various other companies. Initial disclosures of this material, previously known as Firemaster 935, describe in detail the advantages of using this product in polyamide and polyester applications. See, for example, R. C. Nametz et al., 25 SOC. PLAST. ENG. TECH.PAP., 488-91 (1979); P. H. Burleigh et al., 7(1) J. FIRE RETARD. CHEM. 47-57 (1980); and P. H. Burleigh et al., 4 PROC. INT. CONF. FIRE SAF. 279-93 (1979).
The condensation products of brominated phenols are made by various processes involving either aqueous-based processes or two-phased water-solvent processes. U.S. Pat. No. 4,141,880 discloses processes which are organic solvent-aqueous based. Initiators such as benzoyl peroxide are used to initiate polymerization of the brominated phenolates using water and an organic solvent such as chloroform or 1,2,4-trichlorobenzene.
U.S. Pat. No. 4,141,880 discloses a flame retarded, non-blooming polyamide composition comprised of a condensation product derived from brominated phenols and phenolates. These compositions provide a material having good thermal stability. The patent focuses on polyamide compositions. In the processes disclosed a number of solvents are discussed and tetrahydrofuran is mentioned, but the focus is on organic-aqueous based reaction systems or the use of other high-boiling solvents. The advantages of using tetrahydrofuran, recognized by the present invention, were not recognized and presented in any manner in this patent.
In 3 NIPPON KAGAKUKAI SHI 403-08 (1977) a method is discussed in which copper (II) salts are used as catalysts for the condensation polymerization of 2,4,6-tribromophenol catalyzed by the DMF-CuCl2 complex. Several solvents and bases are described for this process. Tetrahydrofuran is disclosed as being used in the purification of the product. The crude polymerization product is precipitated into acidic methanol. The product is purified by dissolving the crude product in tetrahydrofuran. The solution is then filtered and the product re-precipitated into methanol.
Japan Application Number 06-068433 discloses a process to prepare brominated polyphenylene ether wherein a brominated phenolate in water is polymerized with an initiator system comprising a halogenated organic compound that becomes cationic in a nitric acid or silver nitrate reaction.
All disclosed methods to make the polymer suffer from having the polymer precipitate from water, trapping impurities, or from the need to water-wash out bromide salts and precipitate the polymer in a selected non-solvent, or the method is simply not practical industrially. A need exists for a process in which the material can be made with low ionic impurities without requiring the separate washing clean-up step.
Certain electrical components are required to withstand increased processing temperatures because of the higher temperature requirements of lead-free solder during the solder reflow process. This is especially true for components that utilize surface-mount technology (SMT). The processing results in component parts sometimes forming bubbles, or blisters on the surface of the part after the reflow process if the materials are not thermally robust.
The current invention provides a thermally stable flame retardant system and reduces some of the adverse effects of processing on the final polymer.